MODERN  METHODS 
OF  PRINTING 


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| Mr)  5 (M  t'ecT  ^ O 


MODERN  METHODS  OF  PRINTING 


iii 


r 


OLD  STYLE  HAND  PRESS 

— Modernized,  and  built  of  iron,  this  press  embodies  the  princi- 
ples of  the  old  wooden  hand  press,  except  that  the  impression 
is  made  by  toggle-joint  leverage  instead  of  the  original  screw. 
Now  used  almost  wholly  for  “pulling  proofs.” 


GALLEY  PROOF  PRESS 

A rudimentary  style  of  apparatus  used  for  galley  proofs  of  type 
and  relief  plates.  When  the  matter  is  inked  and  the  sheet 
laid  on,  the  large  roller,  covered  with  felt  and  resting  on  side 
ledges,  is  rolled  over  the  face  of  the  form. 


IV 


MODERN  METHODS  OF  PRINTING 


THE  “POTTER”  PROOF  PRESS 

A modern  appliance,  with  cylinder  and  flat  bed,  for  taking  proofs 
of  typographic  forms,  relief  plates,  etc.  Several  styles  of  this 
press  are  made,  some  having  self-inking  apparatus  and  feed- 
table  with  guides  for  securing  close  register  on  color  plates. 


MODERN  METHODS  OF  PRINTING 


V 


THE  “GORDON  ” PLATEN  PRESS 

A popular  style  of  machine  for  small  typographic  work  ; the 
mechanical  principle  invented  about  1858,  and  since  then  em- 
bodied in  various  presses  by  different  manufacturers. 


THE  UNIVERSAL”  PLATEN  PRESS 

A later  invention  than  the  “Gordon,”  different  in  several  im- 
portant particulars,  and  strongly  built  for  heavy  work. 


VI 


MODERN  METHODS  OF  PRINTING 


INTAGLIO  PLATE  PRINTING  PRESS 

Known  as  the  D-roller  press,  because  of  the  form  of  its  im- 
pression section,  this  having  a curved  surface.  The  en- 
graved plate  is  attached  to  the  bed  which  rests  upon  the 
larger  cylinder  underneath  and  carries  it  under  the 
O-shaped  roller  held  firmly  between  the  side  posts 
above  the  bed. 


MODERN  METHODS  OF  PRINTING 


vii 


THE  “DRUM  ” CYLINDER  TYPOGRAPHIC  PRESS 
In  which  the  cylinder  makes  one  revolution  for  each  impression. 
The  large  cylinder  prints  with  only  part  of  its  surface,  then  rises 
slightly  and  continues  its  revolution  while  the  bed,  containing  the 
printing  form,  returns  for  the  next  impression. 


THE  “TWO-REVOLUTION”  CYLINDER 
In  which  the  cylinder  makes  one  revolution  for  the  impression  and 
then,  rising  slightly,  makes  another  revolution  without  impression, 
while  the  bed  is  returning  for  the  next  impression. 


MODERN  METHODS  OF 


PRINTING 


BRIEF  DESCRIPTIONS  OF  THE  RELIEF 
SURFACE,  INTAGLIO  SURFACE,  AND 
LITHOGRAPHIC  PRINTING  PROCESSES 
WITH  SOME  NOTES  ON  PRINTING 
PAPER  AND  INKS 


BY 


A.  A.  STEWART 


THE  SCHOOL  OF  PRINTING 
NORTH  END  UNION,  BOSTON 
1913 


Copyright,  1913,  by 
Alexander  A.  Stewart. 


MODERN  METHODS  OF  PRINTING 


THE  term  Printing  is  applied  to  a great  vari- 
ety of  processes  for  reproducing  flat  decora- 
tions, pidtures,  and  word-matter,  by  mechanical 
means.  The  patterns  on  wall  paper,  calico,  and 
pottery,  and  even  the  pictures  made  from  photo- 
graphic negatives,  are  often  said  to  be  printed. 
For  the  present  purpose,  however,  the  term  is 
limited  to  such  work  as  is  produced  by  applying 
ink  or  color  to  a prepared  surface  and  transfer- 
ring this  color  to  paper,  card,  or  other  equivalent 
material  by  pressure.  The  power  of  multiplying 
copies  is  usually  associated  with  the  idea  of  print- 
ing, which  excludes  typewriting. 

In  printing,  three  different  methods  are  com- 
monly employed,  each  a separate  craft,  distindt 
in  theory,  process,  and  application.  These  are 
known  as : 

The  Relief  Method,  the  chief  part  of  which 
is  typography,  or  printing  from  types.  This  in- 
cludes also  wood  blocks  and  metal  plates  en- 
graved in  high  relief,  like  wood-engravings,  zinc 
line-plate  etchings,  and  halftone  engravings. 

The  Intaglio  Method,  by  which  the  print- 
ing is  done  from  polished  plates  having  the  lines 


4 


MODERN  METHODS  OF  PRINTING 


cut  in  the  surface  and  filled  with  ink.  This 
method  includes  copperplate  and  steelplate  en- 
graving, copperplate  etching,  photogravure,  dry- 
point,  aquatint,  and  mezzotint  engraving,  etc. 

The  Lithographic  Method,  chief  of  which 
is  lithography,  or  printing  from  stone.  This  in- 
cludes also  zincography  (printing  from  metal), 
the  several  photo-gelatin  processes,  and  the  rub- 
ber offset  process. 

THE  RELIEF  METHOD 

In  the  relief  method  of  printing  the  parts  which 
carry  the  ink,  and  make  the  print,  stand  in  relief 
above  the  substance  out  of  which  they  are  made, 
the  parts  which  show  white  being  cut  away  so 
that  no  mark  is  made  on  the  sheet. 

Typography,  or  letter-press  printing,  is  the 
method  of  printing  from  movable  types  having 
letters  and  other  characters  cast  in  high  relief. 
The  types  are  independent  of  each  other,  but  so 
made  that  they  may  be  arranged  in  endless  com- 
binations, and  after  being  once  used  for  one  line 
or  page  may  be  separated  and  re-assembled  to 
print  other  lines  and  other  pages.  Other  methods 
of  relief  printing  require  the  engraving  or  prep- 
aration of  the  subject  by  slow  processes  upon 
the  printing  surface,  which,  when  once  made, 
cannot  readily  be  used  for  anything  else.  A page 
of  type,  however,  may  be  composed,  corrected, 
locked  up  for  a press,  and  impressions  made  in 


MODERN  METHODS  OF  PRINTING 


5 


an  hour  or  less.  This  may  be  done  after  little 
practice  by  any  intelligent  person,  with  mate- 
rials which  may  be  readily  obtained  in  all  com- 
mercial centers.  The  page  also  may  be  as  readily 
molded,  and  this  mold  used  to  produce  a dupli- 
cate printing  form  in  one  piece  of  thin  metal. 
For  the  great  bulk  of  book  printing  this  duplicate, 
called  an  electrotype,  is  employed.  In  this  way 
types  sufficient  to  set  up  a few  pages  of  this 
book  may  be  composed,  corrected,  and  the  pages 
locked  up  and  molded,  then  the  types  distributed 
and  set  again  for  other  pages  of  the  same  work, 
continuing  the  process  for  any  number  of  pages. 
The  surface  of  type  forms  can  also  be  multiplied 
by  the  stereotype  process,  which  is  the  method 
now  employed  for  nearly  all  daily  newspapers,  as 
it  is  the  quickest  and  permits  of  casting  plates  in 
a curved  form,  so  that  they  may  be  fastened  to 
the  cylinders  of  fast  rotary  printing  machines. 

Up  to  about  thirty  years  ago  type-setting  was 
done  almost  entirely  by  hand  work,  but  since 
that  time  type-composing  machines  have  been 
developed  so  skillfully  that  the  greater  part  of 
plain  composition  on  newspaper,  periodical,  and 
book  work  is  now  done  with  machines. 

ENGRAVING  PROCESSES 

Closely  related  to  typography  in  modem  practice 
are  wood  engravings,  line-plate  etchings,  and 
halftone  etchings.  Engravings  of  these  kinds  are 


6 


MODERN  METHODS  OF  PRINTING 


in  relief,  and  when  made  on  blocks  which  bring 
their  surface  to  the  height  of  type  they  may  be 
put  in  the  same  forms  with  type,  or  in  separate 
forms,  and  printed  on  an  ordinary  typographic 
press.  The  wood-cut  is  the  older  style  of  engrav- 
ing, but  because  of  the  slow  hand-work  and  its 
greater  cost  it  has  been  superseded  by  the  zinc 
line-plate  and  the  copper  halftone. 

The  zinc  etching,  or  process  block,  is  made  by 
chemical  and  mechanical  means  and  is  exten- 
sively used  for  many  kinds  of  printing.  In  making 
the  plate,  the  design  is  photographed  upon  a film 
of  bichromated  fish  glue  or  albumen,  which  is 
afterward  spread  upon  a plate  of  zinc.  This  film, 
after  some  manipulation,  is  used  as  a coating  to 
resist  the  action  of  an  etching  acid.  Where  the 
film  remains  the  surface  of  the  zinc  is  unchanged, 
and  where  the  film  is  absent  the  zinc  is  etched 
away.  In  this  manner  the  face  of  the  plate  is 
eaten  away  in  the  white  parts  and  the  dark  parts 
are  left  in  relief. 

The  copy  for  reproduction  is  usually  drawn  on 
white  cardboard  with  perfectly  black  ink,  and  all 
tones  of  light  and  shade  are  rendered  in  definite 
spots  and  lines  of  varying  sizes.  Grained  surfaces 
may  also  be  reproduced. 

Halftone  engraving  is  now  the  most  widely 
used  method  of  illustration.  It  is  done  by  opera- 
tions similar  to  the  zinc  etching  process.  The 
essential  difference  is  the  use  of  a lined  or  grained 


MODERN  METHODS  OF  PRINTING 


7 


screen  interposed  when  photographing  the  copy. 
This  screen  is  placed  near  the  camera  plate  and 
the  picture  is  broken  up  into  a mass  of  small  dots. 
The  resulting  negative  is  then  placed  beside  a 
sensitized  copper  plate,  and  after  another  expos- 
ure the  picture  is  transfered  to  the  copper,  which 
is  then  developed  and  etched  with  acid. 

A screen  of  60  to  80  lines  to  the  inch  is  suited 
for  the  rapid  work  and  cheap  paper  of  daily  news- 
papers; screens  of  135  to  200  lines,  for  smooth 
coated  papers  printed  on  slower  presses,  give  the 
fine  results  seen  in  commercial  and  periodical 
printing.  The  finer  the  screen,  the  shallower  the 
plate  can  be  etched,  therefore  the  paper  must  be 
smooth  and  the  ink  fine  in  order  to  print  clearly. 

PRESSWORK 

Relief  printing  is  done  on  machines  of  two  dis- 
tinct classes  ; the  platen,  or  flat  surface,  and  the 
cylinder.  The  old  hand  press  consisted  of  a flat 
bed  upon  which  the  type-form  was  placed  ; after 
being  inked  and  the  sheet  laid  on,  the  form  was 
subjected  to  impression  by  another  plane  sur- 
face. The  modern  platen  press  embraces  the 
same  principle  with  the  operations  applied  me- 
chanically instead  of  by  hand  labor.  Cylinder 
presses  are  of  two  classes.  One  style  consists  of 
a flat  bed  holding  the  printed  form,  which  passes 
back  and  forth  beneath  a revolving  cylinder 
carrying  the  sheet  and  giving  the  impression. 


8 


MODERN  METHODS  OF  PRINTING 


The  other  consists  of  two  facing  cylinders,  on 
one  of  which  a curved  printing  form  is  placed ; 
the  other  cylinder,  having  a smooth  surface,  im- 
parts the  impression  as  the  sheet  passes  between 
the  two  cylinders  revolving  in  opposite  directions. 
This  latter  style  of  press  is  the  kind  employed 
for  daily  newspapers,  large  edition  periodicals, 
and  advertising  matter  issued  in  large  quantities. 
The  flat-bed-and-cylinder  style  of  machine  is  the 
kind  in  most  common  use  for  book  and  com- 
mercial work.  It  is  made  in  many  varieties  by 
different  manufacturers,  and  is  the  kind  upon 
which  the  largest  part  and  the  best  grades  of 
typographic  printing  are  done.  The  mechanical 
platen  press  is  used  for  jobbing  and  miscella- 
neous small  work,  while  the  hand  press  is  largely 
employed  for  taking  proofs  of  type  and  engrav- 
ings, and  for  work  of  which  only  few  copies  are 
required. 

THE  INTAGLIO  METHOD 

By  the  intaglio  method  of  printing  the  design  is 
cut  in  the  surface  of  the  plate,  the  lines  or  dots 
thus  engraved  being  filled  with  the  ink,  the  face 
of  the  plate  then  wiped  clean,  and  the  paper, 
slightly  damp,  pressed  on  the  plate  under  the 
curved  surface  of  a roller  press.  By  this  pres- 
sure the  paper  is  forced  into  the  sunken  lines 
and  takes  up  the  ink,  so  that  the  printing  has  a 
slightly  embossed  or  raised  appearance.  This 


MODERN  METHODS  OF  PRINTING 


9 


method  is  in  every  respedt  the  reverse  of  print- 
ing from  type,  and  gives  results  in  delicacy  of 
line  and  brilliance  and  depth  of  color  not  obtain- 
able by  other  methods.  The  ink  fills  the  lines  in 
a compact  body  and  does  not  spread  out  under 
pressure;  whereas  with  type  the  pressure  of 
printing  from  a fine  line  covered  with  ink  tends 
to  weaken  the  color  and  leave  blurred  edges. 

There  are  several  methods  of  engraving  on 
copper  and  steel  plates,  each  employed  accord- 
ing to  the  nature  of  the  design.  The  engraving 
is  done  by  hand  with  sharp  tools,  or  gravers,  pro- 
ducing precise  lines  of  varying  thickness,  as  for 
script  lettering.  A succession  of  uniform  lines, 
straight,  curved,  or  waved,  are  made  on  a ruling 
machine,  and  stippling  is  done  by  minute  punc- 
tures, the  dots  being  larger  or  smaller,  close  or 
open,  to  give  varying  tones  of  color,  Another 
method  is  to  etch  the  surface  with  a corroding 
acid.  The  plate  is  covered  with  a coating  through 
which  the  design  is  cut,  and  the  metal  afterward 
eaten  away  where  it  is  exposed.  Because  of  its 
greater  freedom  of  manipulation,  its  quickness, 
in  comparison  with  the  hand  engraving  method, 
and  the  sketchy  nature  of  etched  lines,  this  latter 
method  is  popular  with  artists,  and  is  employed 
largely  for  wall  pictures  and  works  of  art. 

Copper-  and  steel-plate  printing,  being  almost 
entirely  hand-work  and  not  easily  adaptable  to 
rotary  or  other  mechanical  methods,  is  slow  and 


10 


MODERN  METHODS  OF  PRINTING 


costly.  The  kinds  of  work  done  are  chiefly  per- 
sonal cards,  wedding  and  society  cards,  announce- 
ments, and  stationery. 

The  presses  used  are  not  at  all  like  those  used 
for  printing  type  forms  and  relief  plates.  Each 
print  requires  the  ink  to  be  worked  into  the  en- 
graved lines,  the  surplus  ink  cleaned  from  the 
face  of  the  plate,  the  sheet  laid  on,  and  the  im- 
pression taken.  The  output  of  a single  press  is 
limited  to  a few  hundred  copies  a day.  This 
method  is  the  same  now  as  when  it  was  first  in- 
vented in  the  fifteenth  century.  The  tools  are 
the  same ; the  D -roller  press  is  practically  the 
same,  perhaps  better  made ; the  workman  wipes 
off  his  plate  in  the  same  way.  In  bank-note 
printing  and  a few  special  lines  of  work  new 
machines  have  been  introduced,  but  a great  part 
of  this  kind  of  work  is  today  done  by  the  original 
hand  methods. 

Steel-plate  printing  employs  practically  the 
same  methods  as  copper  plate  work,  the  engrav- 
ing being  done  on  a plate  of  polished  steel  instead 
of  copper.  The  method  is  used  for  bank  notes, 
postage  stamps,  etc.,  and  was  formerly  largely 
used  for  portraits  and  fine  illustrations,  though 
for  this  latter  purpose  halftones  and  photograv- 
ures have  now  largely  superseded  steel  plates, 
because  of  the  smaller  cost. 

Steel  dies  for  stamping  note  paper,  envelopes, 
and  similar  work,  are  also  manipulated  by  the 


MODERN  METHODS  OF  PRINTING 


11 


same  general  methods.  The  steel  is  soft,  so  that 
it  can  be  cut  without  much  difficulty  with  hand 
tools.  After  the  engraving  is  done,  the  steel  is 
put  through  a hardening  process,  to  prepare  it 
for  withstanding  the  wear  of  printing.  As  the 
design  is  sunk  in  the  metal,  it  is  necessary  to 
use  a counter  die  to  force  the  paper  into  the  sunk- 
en parts  to  take  up  the  ink.  The  impression  from 
an  engraving  of  this  kind  will  show  the  printed 
design  raised  in  distinct  relief  on  the  surface  of 
the  paper.  The  counter  die  is  made  usually  of 
a substance  known  as  tar-board,  a piece  of  which 
is  laid  on  the  steel  die  and  a strong  impression 
taken.  The  edges  of  the  tar-board  are  then  trim- 
med away  gradually  up  to  the  face  of  the  design, 
so  that  the  impression  will  be  chiefly  at  the 
actual  point  of  printing. 

Die  printing  is  commonly  done  with  a stamp- 
ing press  operated  by  hand,  but  there  are  now 
several  embossing  and  die-stamping  presses  in 
which  most  of  the  operations  are  automatic,  and 
the  inking  and  wiping  of  the  die  is  done  mechan- 
ically instead  of  by  hand. 

PHOTOGRAVURE  PRINTING 

One  of  the  most  popular  and  beautiful  reproduc- 
tive methods  for  illustrative  purposes  is  the  in- 
taglio process  known  as  photogravure.  There  are 
numerous  variations  in  the  details  of  this  process 
as  carried  on  by  different  operators,  but  in  a gen- 


12 


MODERN  METHODS  OF  PRINTING 


eral  way  the  method  is  by  chemically  treating  a 
gelatin,  albumen,  or  asphaltum  film,  upon  which 
the  subject  has  been  photographically  fixed,  on 
a metal  printing  plate. 

The  metal  plate,  which  is  usually  a sheet  of 
polished  copper  free  from  all  traces,  of  grease, 
etc.,  is  prepared  by  graining ; that  is,  a finely 
powdered  resin  dust  is  deposited  on  the  surface 
of  the  plate  and  fixed  by  heating,  so  that  the 
particles  form  a slightly  rough  or  grained  ground. 
On  this  ground  a photographic  film  is  placed  and 
manipulated  in  such  a manner  that  the  different 
parts  of  the  picture  are  represented  by  differences 
in  the  thickness  of  the  gelatin.  The  light  parts 
of  the  picture  are  represented  by  the  greatest 
thickness,  the  half  tones  by  lesser,  and  the  dark 
parts  by  the  thinnest  film.  The  plate  is  painted 
on  the  back  and  sides  by  an  acid-resisting  var- 
nish and  placed  in  an  etching  bath.  The  face  of 
the  plate  is  thus  etched  by  the  strong  acid.  Where 
the  gelatin  is  thinnest  the  acid  etches  deepest, 
and  where  it  is  thickest  the  copper  is  etched 
least.  Sometimes  hand  work  is  necessary  on  the 
plate,  to  smooth  down  the  light  parts  by  burnish- 
ing or  scraping  the  copper,  by  adding  detail,  or 
intensifying  the  dark  parts  by  cutting  into  the 
copper  with  a fine  tool  or  small-toothed  wheel. 

As  the  soft  copper  used  is  not  durable  enough 
to  withstand  the  wear  of  a large  number  of  im- 
pressions, the  plate  is  usually  steel -faced  by  giv- 
ing it  an  electrolytic  coating  of  steel. 


MODERN  METHODS  OF  PRINTING 


13 


In  printing,  the  ink  is  forced  by  means  of  a 
dabber  or  roller  into  the  hollows  etched  into  the 
plate  and  the  surplus  ink  wiped  from  the  upper 
surface  and  the  margins.  In  the  grain  all  over 
the  plate  are  little  points  or  teeth  of  copper  where 
the  particles  of  resin  dust  were  burned  on,  and 
these  hold  the  ink  and  prevent  it  from  being 
wiped  away  from  the  hollow  spaces  when  the 
surplus  ink  is  cleared  off.  Damp  paper  is  then 
laid  on  the  plate,  backed  with  blanketing,  and 
the  impression  made  by  means  of  a heavy  iron 
roller  in  a special  hand  press. 

Machine-printed  photogravure  work  is  being 
developed  to  some  extent,  and  some  work  of  this 
kind  has  been  done  from  curved  surfaces ; but, 
like  other  copperplate  work,  the  bulk  of  photo- 
gravure printing  is  done  on  hand  presses. 

THE  LITHOGRAPHIC  METHOD 

Under  the  head  of  the  plane-surface  method  of 
printing,  the  chief  process  is  lithography,  or  print- 
ing from  flat  stones.  There  are  several  proc- 
esses closely  allied  to  this,  in  which  surfaces 
other  than  stone  are  used,  such  as  zinc,  alumi- 
num, rubber,  gelatin,  etc. 

The  theory  of  lithographic  printing  is  based 
upon  the  repulsion  of  grease  and  water,  and  the 
production  of  the  design  depends  upon  chemical 
manipulation  of  the  printing  surface.  The  kind 
of  stone  employed  is  a fine  limestone  which  has 


14 


MODERN  METHODS  OF  PRINTING 


a natural  affinity  for  grease.  The  design  to  be 
printed  is  put  on  the  stone  with  specially  pre- 
pared fatty  inks,  which  dry  on  the  surface  of  the 
stone  and  render  that  part  insoluble  in  water  or 
spirits  and  is  durable  even  under  considerable 
friction.  The  surface  is  then  subjected  to  the 
action  of  a weak  acid  which  slightly  etches  or 
roughens  the  blank  portions,  after  which  it  is 
washed  with  gum  arabic  to  give  these  parts  a 
slight  grease-resisting  quality. 

The  preparation  of  the  design  on  the  stone 
may  be  done  in  several  ways:  by  drawing  it  on 
with  a special  crayon,  or  pencil,  or  with  pen  and 
lithographic  ink ; and  by  writing,  drawing,  print- 
ing, or  photographing  on  prepared  paper  and 
then  transferring  this  to  the  stone. 

LITHOGRAPHIC  PRESSWORK 

The  process  of  printing  from  lithographic  stone 
requires  moistening  the  surface  with  water, 
which  is  absorbed  by  the  blank  parts  and  repelled 
by  the  hard,  greasy  lines  of  the  design.  The 
printing  ink  is  then  applied  and  is  repelled  by  the 
wet  parts  but  adheres  readily  to  the  lines  and 
spots  of  the  design.  The  stone  thus  prepared  is 
ready  to  make  its  impression  on  the  paper. 

Like  other  methods  of  printing,  lithographic 
work  was  formerly  done  on  hand  presses,  but 
since  1860  power  presses  have  been  invented 
and  many  improved  details  have  been  employed. 


MODERN  METHODS  OF  PRINTING 


15 


The  lithographic  hand  press  has  a movable  bed, 
like  that  of  the  typographic  hand  press,  but  the 
impression  is  made  with  a straight-edge  scraper 
at  the  press-head,  instead  of  with  a flat  platen. 
The  bed  moves  under  this  scraper,  which  extends 
across  the  width  of  the  stone  and  imparts  great 
pressure  on  a small  area  at  a time. 

The  first  operation,  when  printing,  is  to  moist- 
en the  surface  so  that  the  subsequent  inking  will 
leave  the  ink  only  on  the  design.  When  sufficient 
ink  has  been  applied,  the  sheet  is  laid  on,  the 
tympan  turned  down,  and  the  bed  moved  in  un- 
der the  scraper.  The  back  of  the  tympan  is  of 
leather,  zinc,  or  brass,  and  is  slightly  lubricated 
to  allow  the  scraper  to  pass  over  it  with  as  little 
friction  as  possible.  Lithographic  ink  rollers  are 
made  by  covering  wooden  or  iron  cores  with  felt 
or  flannel,  the  outside  inking  surface  being  a fine 
grained  or  glazed  calf  leather. 

Lithographic  power  presses  are  similar  to  cyl- 
inder presses  used  for  typographic  work,  but  with 
some  necessary  differences  in  detail  of  construc- 
tion. A lithographic  stone,  after  being  used,  may 
be  ground  down  and  have  a fresh  surface  pre- 
pared for  another  design.  Thus,  different  thick- 
nesses of  stones  must  be  used,  and  the  distance 
between  the  bed  and  the  cylinder  must  be  varied 
to  accommodate  these  differences.  The  cylinder 
is  covered  with  a thick,  elastic  blanket  or  sheet  of 
indiarubber.  The  necessary  moisture  is  applied 


16 


MODERN  METHODS  OF  PRINTING 


to  the  stone  by  wet  rollers,  which  are  at  the  op- 
posite end  of  the  press  from  the  inking  rollers. 
These  wet  rollers  consist  of  cores  wound  with 
several  thicknesses  of  flannel  and  covered  on  the 
outside  with  cotton  or  linen  fabric. 

Chromo-lithography  is  the  process  by  which  a 
picture  is  printed  in  several  colors.  A separate 
stone  is  used  for  every  color  printed,  and  in  re- 
producing paintings  of  many  colors  the  skill  of 
the  lithographic  draftsman  consists  in  his  selec- 
tion of  such  colors  as  will  reproduce  the  original 
in  the  fewest  printings.  The  comparative  ease 
with  which  transfers  may  be  made  from  one 
stone  to  another,  and  the  accuracy  which  may 
be  secured  in  registering  a number  of  colors 
over  each  other,  have  especially  adapted  lithog- 
raphy for  color  work. 

Stones  of  good  quality  for  lithographic  work 
are  becoming  more  and  more  difficult  to  obtain, 
so  that  zinc  and  aluminum,  suitably  prepared, 
are  now  largely  used  instead.  These  thin  metal- 
lic surfaces  have  the  great  advantage  of  being 
adapted  to  the  curved  surfaces  of  rotary  ma- 
chines, and  therefore  the  printing  may  be  done 
at  high  speeds. 

GELATIN  PRINTING 

A printing  process  analogous  with  lithography 
is  known  as  collotypy,  in  which  a film  of  gelatin 
deposited  on  a ground  glass  or  metallic  surface 


MODERN  METHODS  OF  PRINTING 


17 


is  used  instead  of  stone.  The  basis  is  a thick 
glass  plate  coated  with  a gelatin  film  containing 
a bichromate.  This  is  dried  in  the  dark.  The 
design  is  put  on  this  gelatin  surface  by  means  of 
a photographic  negative,  and  the  film  is  affected 
by  light  in  its  different  parts  according  to  the 
lights  and  shades  of  the  pidture.  Where  rays  of 
light  strike  this  sensitive  film,  that  part  becomes 
more  or  less  insoluble  and  will  refuse  to  absorb 
water,  while  the  parts  which  have  not  been 
exposed  will  remain  absorbent.  The  exposed 
film  is  then  washed  and  dried  out  again,  and 
again  dampened  with  a solution  of  glycerin  and 
water,  which  is  absorbed  by  the  light  parts  and 
repelled  by  the  dark  parts.  When  thus  prepared, 
a roller  containing  greasy  ink  is  passed  over  the 
gelatin  surface  ; the  ink  will  adhere  to  the  insol- 
uble parts  and  refuse  to  stay  on  the  damp  parts, 
similar  to  the  action  of  inking  a lithographic 
stone.  The  printing  is  done  on  a small  appara- 
tus like  a lithographic  hand  press.  The  gelatin- 
covered  plate  rests  on  a bed  to  which  a thin  brass 
or  other  metallic  tympan-frame  is  hinged.  After 
inking  and  laying  on  the  sheet,  this  tympan  with 
its  necessary  blanketing  is  turned  down  and  the 
bed  drawn  under  a straight-edge  scraper  which 
covers  the  width  of  the  plate, 

Printing  with  gelatin  surfaces  gives  the  fine, 
soft  effects  of  photography,  with  the  permanence 
of  colored  pigments.  Being  almost  entirely  hand 


18 


MODERN  METHODS  OF  PRINTING 


work,  it  is  necessarily  slow  and  expensive,  and 
is  employed  only  for  small  editions. 

Slight  variations  of  the  gelatin  lithographic 
process  are  known  by  other  names,  such  as  helio- 
type, albertype,  phototype,  autoglyph,  etc. 

THE  OFFSET  METHOD 

This  method  of  printing  has  recently  undergone 
rapid  development,  especially  in  this  country.  It 
is  one  of  the  variations  of  the  lithographic  prin- 
ciple, employing  a flat  surface,  chemically  treated, 
for  holding  the  design  to  be  printed,  and  a rotary 
machine  with  three  cylinders  for  the  printing 
operations.  One  cylinder  carries  a zinc  plate  con- 
taining the  design,  transferred  from  an  original 
copy ; this  cylinder  prints  on  the  rubber  covering 
of  a second  cylinder,  which,  after  receiving  the 
impression,  prints,  or  offsets,  on  to  the  sheet  of 
paper  that  is  carried  around  by  the  third,  or  im- 
pression, cylinder.  Two  sets  of  rollers  are  used, 
adjusted  close  to  the  cylinder  holding  the  zinc 
plate.  One  set  of  rollers  supplies  ink  to  the  plate, 
while  the  other  set  dampens  it,  as  in  ordinary 
lithography. 

THE  THREE-COLOR  PROCESS 

This  is  a method  of  reproducing,  photo-mechan- 
ically,  with  only  three  printing  plates,  a picture 
or  drawing  in  any  number  of  colors.  The  process 
includes  making  three  photographic  negatives  of 


THE  SCOTT  ROTARY  OFFSET  PRESS 
with  sheet-feeding  attachment 


MODERN  METHODS  OF  PRINTING 


19 


the  copy  to  be  reproduced.  Each  of  these  nega- 
tives is  then  used  to  make  a halftone  plate  which 
will  print  one  of  the  three  primary  colors.  The 
three  colors,  yellow,  red,  and  blue,  are  used  be- 
cause their  mixture  in  varying  proportions  will 
produce  all  other  colors  of  the  spectrum. 

In  making  these  negatives,  colored  screens  or 
filters  are  used  between  the  negatives  and  the 
copy.  For  the  negative  used  to  make  the  yellow 
plate  a colored  filter  is  employed  to  shut  out  the 
yellow  rays  and  allow  only  the  red  and  blue  rays 
to  pass  through  and  affect  the  film.  For  the  red- 
plate  negative  another  filter  admits  only  the  blue 
and  yellow  rays,  and  for  the  blue-plate  negative 
a filter  admits  only  the  yellow  and  red  rays. 
From  these  negatives  other  films  are  made,  and 
these  in  turn  are  used  to  make  halftone  plates. 

The  halftone  plates  are  then  printed  one  over 
the  other  in  prescribed  order.  When  rolled  with 
an  ink-roller  holding  ink  of  the  required  color, 
the  etched  surface  of  each  halftone  plate  takes 
on  its  different  parts  just  the  right  amount  of  ink 
to  combine  with  the  colors  printed  by  the  other 
plates  and  produce  the  effect  in  the  original. 

A fourth  color  plate  may  be  added  and  the 
blue  plate  of  the  three-color  series  printed  in  a 
paler  blue,  using  the  fourth  plate  to  print  black 
over  the  other  three  colors. 

Great  skill  is  required  to  make  the  plates,  and 
they  require  more  or  less  special  attention  in 


20 


MODERN  METHODS  OF  PRINTING 


etching  different  parts  in  order  to  obtain  correct 
color  values.  Expert  skill  is  required  also  in  the 
printing  of  the  plates  to  produce  good  results  — 
just  the  right  color  and  quantity  of  ink,  just  the 
right  impression  on  each  part,  and  absolutely 
exact  register;  for,  while  many  of  the  halftone 
dots  in  the  plates  must  be  printed  over  each  other 
to  give  the  darker  colors  of  the  picture,  in  the 
lighter  parts  the  smallest  dots  in  one  plate  must 
be  printed  between  and  beside  those  of  another 
plate  without  overlapping  or  smudging. 

Color  work  is  sometimes  done  with  two  half- 
tone plates,  or  with  one  halftone  and  a flat  tint 
block,  registered  over  each  other,  giving  two 
tones  of  one  color  or  two  contrasting  colors. 

OTHER  METHODS  OF  ENGRAVING 

Wax  Engraving.  A common  method  for  making 
printing  plates  for  maps,  charts,  diagrams,  and 
other  classes  of  work.  It  is  less  expensive  than 
other  methods  of  engraving,  and  may  be  done 
quickly.  A polished  plate  of  copper  or  brass  is 
covered  with  a thin  film  of  specially  prepared 
wax,  and  upon  this  the  design  may  be  made 
either  by  photography,  hand  drawing,  or  other 
transfer  method.  The  engraving  of  the  wax  sur- 
face is  done  by  sharp-pointed  tools,  a ruling  ma- 
chine, or,  in  the  case  of  lettering,  ordinary  types 
are  pressed  in  the  warm  wax,  one  letter  or  one 
word  at  a time.  In  this  manner  the  wax-covered 


MODERN  METHODS  OF  PRINTING 


21 


plate  becomes  a mold,  the  large  blank  spaces  are 
“ built  up  ” in  the  same  manner  as  an  electrotype 
wax  mold,  and  it  is  then  put  in  an  electric  bath 
and  a copper  shell  deposited  on  its  face.  A print- 
ing plate  is  made  by  the  same  general  procedure 
as  with  an  ordinary  electrotype. 

Chalk-Plate  Engraving.  This  is  a quick,  cheap 
method  of  making  simple  relief  plates  for  illus- 
trative purposes.  The  picture  or  design  is  drawn 
on  a steel  plate  coated  with  a chalk  preparation. 
The  drawing  is  done  with  a fine  steel-pointed 
tool,  which  cuts  through  the  chalk  all  the  lines 
it  is  desired  to  print.  The  plate  is  then  used  as  a 
matrix  and  stereotype  metal  cast  from  it,  which 
results  in  a stereotype  block  with  the  engraved 
lines  standing  in  relief  on  its  surface.  This 
method  depends  upon  the  skill  of  the  draftsman 
who  must  do  his  work  largely  freehand,  and  it 
is  not  easily  adapted  for  fine  or  exact  lines. 

MANUFACTURE  OF  PAPER 

Printing  papers  are  made  from  several  varieties 
of  vegetable  fiber,  those  most  commonly  used  be- 
ing linen  and  cotton  rags,  hemp,  jute,  and  wood. 
The  raw  material  necessary  for  paper  is  cellu- 
lose, the  indestructible  cell-membrane  of  plants. 
The  quality  of  paper  is  dependent,  first,  upon  the 
quality  of  the  cellulose,  and  next,  upon  the  man- 
ner in  which  it  is  manufactured.  As  cotton  fiber 
contains  the  greatest  amount  of  pure  cellulose,  it 


22 


MODERN  METHODS  OF  PRINTING 


makes  the  best  paper.  The  great  bulk  of  paper 
in  common  use,  however,  is  made  of  wood. 

After  the  raw  material  is  sorted  and  cut  up,  the 
process  is  continued  by  grinding,  bleaching,  beat- 
ing, and  boiling  until  the  fibers  are  reduced  to  a 
soft  pulp.  As  it  was  made  by  hand  in  early  days, 
this  pulp  was  dipped  from  a vat  with  a shallow 
mold  having  a screen  bottom.  When  the  water 
drained  away,  the  remaining  film  of  interlaced 
fibers  was  deftly  turned  out,  pressed,  and  dried. 
Hand-made  paper  is  still  produced  in  small  quan- 
tities for  special  editions  of  fine  books,  note  paper, 
etc.,  but  the  process  is  so  laborious  and  costly  that 
its  use  is  necessarily  limited. 

Paper  is  now  made  almost  entirely  by  elabo- 
rate machinery,  in  which  the  prepared  pulp  flows 
on  to  a frame  or  cloth  of  fine  wire  that  moves 
continually  forward  on  rollers.  This  wire  frame 
has  a shaking  motion  and  allows  the  water  to 
escape  while  holding  the  fibers  evenly  spread  out. 
As  the  pulp  passes  along  it  is  taken  up  between 
a pair  of  couch  rolls  which  press  it  into  a self- 
supporting  sheet.  It  next  goes,  in  an  endless 
sheet,  between  press  rolls  and  steam-heated  cyl- 
inders which  dry  it  rapidly.  The  finishing  process 
is  done  in  a variety  of  ways,  according  to  the 
quality  of  the  paper  and  the  nature  of  the  sur- 
face desired. 

Wood  pulp  is  of  two  distindt  classes : mechan- 
ical and  chemical.  The  mechanical  or  ground 


MODERN  METHODS  OF  PRINTING 


23 


pulp  is  made  by  feeding  pieces  of  wood  against  a 
rapidly-revolving  grindstone  over  which  water 
is  flowing.  The  pulp  is  then  screened  in  order  to 
eliminate  splinters  and  chips.  This  product  is 
of  low  quality,  as  it  contains  a great  deal  of  the 
gummy  portions  of  the  original  wood,  and  the 
fibers  are  short  and  inflexible.  The  chemical 
pulp  is  made  by  chipping  the  logs  and  cooking 
the  chips  in  large  digesters  with  strong  liquors 
at  a high  temperature.  After  cooking,  the  pulp  is 
washed,  screened,  and  bleached.  This  process 
dissolves  the  resinous  and  gummy  matters,  and 
leaves  the  cellulose  fibers  in  a practically  pure 
state.  These  fibers  are  much  better  than  the 
ground  wood,  as  they  are  freed  from  substances 
which  soon  decay,  and  are  longer,  stronger,  and 
more  flexible. 

There  are  several  different  kinds  of  chemical 
wood  pulps,  varying  in  character  according  to 
the  kinds  of  wood  used  and  the  cooking  process. 

Mechanical  pulp  and  chemical  pulp  are  often 
used  together,  the  quality  of  paper  depending  on 
the  proportion  of  low  grade  and  better  pulp. 
Wood  pulp  is  also  mixed  with  rag  pulp  for  many 
grades  of  paper,  the  substances  being  used  in 
varying  proportions,  according  to  the  quality  and 
finish  desired.  Rag  stock  and  long-fiber  wood 
pulp  may  have  some  short-fiber  stock  added  to 
fill  up  the  minute  interstices.  Clay  or  other  min- 
eral may  be  added  as  a filler,  to  give  closer  con- 


24 


MODERN  METHODS  OF  PRINTING 


sistency,  smoother  finish,  and  extra  softness  to 
the  sheet.  Mineral  filler  gives  extra  weight. 

Laid  paper  is  made  on  a screen  in  which  the 
wires  are  laid  parallel,  with  a large  wire  crossing 
at  regular  intervals.  The  large  wire-marks  show 
light  lines  when  the  sheet  is  held  to  the  light. 

Wove  paper  is  made  on  a frame  in  which  fine 
wires  are  woven  together  like  the  threads  of  or- 
dinary cloth.  Distinct  wire-marks  do  not  show, 
as  in  laid  paper.  Most  printing  paper  is  now 
made  on  this  kind  of  a frame,  as  the  wire-marks 
of  laid  paper  are  liable  to  show  in  printing  solid 
or  flat  surfaces. 

Laid  and  wove  papers  differ  only  in  the  wire- 
mark  ; the  same  quality  of  material  may  be  used 
in  both,  although  the  laid  pattern  is  oftener  seen 
in  writing  paper. 

The  device  known  as  a “ water-mark,”  which 
may  be  seen  when  a sheet  is  held  to  the  light,  is 
really  a wire-mark.  It  is  made  when  the  pulp  is 
first  formed  into  a sheet,  in  the  same  way  as  the 
lines  in  “ laid  ” paper,  by  means  of  a wire  device. 
The  paper  is  slightly  thinner  and  more  transpar- 
ent where  the  wire  makes  its  impression. 

A rough,  feather  edge,  known  as  deckle  edge,  is 
formed  where  the  pulp  flows  against  the  “deckle” 
which  keeps  the  pulp  from  running  off  the  sides 
of  the  screen.  This  edge  is  sometimes  left  on  the 
better  grades  of  book  and  cover  paper  intended 
for  special  books  and  pamphlets.  Machine-made 


MODERN  METHODS  OF  PRINTING 


25 


paper  has  this  deckle  edge  on  two  sides  of  the 
whole  sheet,  while  hand-made  paper  has  the 
deckle  on  all  four  sides. 

An  important  difference  in  the  structure  of 
hand-made  and  machine-made  papers  is  the 
grain  or  general  position  of  the  long  fibers.  In 
hand-made  paper  the  fibers  interlace  and  cross 
each  other  in  many  directions,  so  that  the  sheet 
will  usually  fold  both  lengthwise  and  crosswise 
without  showing  a difference  in  the  folding  qual- 
ity or  flexibility  of  the  sheet.  In  machine-made 
paper  the  tendency  of  the  fibers  is  to  assume  the 
direction  in  which  the  pulp  flows  on  to  the  screen, 
so  that  the  paper  has  a distinct  grain  with  the 
fibers  running  in  one  general  direction.  In  many 
grades  of  machine-made  paper  the  flexibility  of 
the  leaves  in  a bound  book  will  depend  upon 
whether  the  grain  runs  across  or  lengthwise  of 
the  page.  Usually  the  fold  should  be  with  the 
,grain,  as  the  paper  bends  smoother  and  makes  a 
more  flexible  hinge  for  the  leaf.  When  folded 
across  the  grain  the  fold  will  show  a rough, 
broken  edge.  In  cover  stock  and  heavy  papers 
the  relation  of  the  fold  to  the  grain  is  often  an 
important  consideration. 

FINISH  OF  PAPER 

Although  the  surface  finish  of  paper  will  make  a 
very  great  difference  in  its  appearance,  it  often 
gives  no  indication  of  its  quality.  Each  kind  of 


26 


MODERN  METHODS  OF  PRINTING 


finish,  however,  is  usually  made  with  a special 
grade  of  stock.  But  sometimes  a cheap  material 
is  given  a fine  finish,  while  the  best  grade  of  raw 
material  may  have  a rough,  unpretentious  finish. 

Clay  is  used  largely  in  printing  paper  to  fill  up 
the  pores  between  the  fibers  and  make  a smoother 
finish.  It  is  objectionable  because  it  adds  greatly 
to  the  weight  and  reduces  the  strength  and  dura- 
bility of  paper. 

There  are  six  usual  styles  of  finish  to  ordinary 
printing  paper:  antique,  machine,  English,  cal- 
endered, smooth  coated,  and  dull  coated. 

Antique  is  a rough  surface,  the  paper  being  left 
light,  bulky,  uncalendered,  and  without  “ filling.” 

Machine  finish  is  the  surface  given  as  the  paper 
passes  between  the  ordinary  machine  rollers,  but 
without  the  final  calender  finish. 

Calendered  paper  is  passed  through  a set  of 
extra  rollers,  or  calenders,  which  subject  it  to  a 
heavy  pressure,  the  degree  of  polish  being  gov- 
erned by  the  number  of  rollers  and  the  amount 
of  pressure. 

So-called  English  finish  is  the  highest  machine 
finish,  the  next  degree  of  smoothness  being  super- 
calendered,  which  is  the  highest  degree  of  finish 
on  an  uncoated  surface. 

Coated  paper  is  a machine-finished  paper  that 
is  covered  (by  a special  operation)  with  a fine 
clay  paste  and  polished  in  a stack  of  friction  cal- 
enders. 


MODERN  METHODS  OF  PRINTING 


27 


Dull  (or  “cameo”)  finish  is  given  by  a clay  coat- 
ing and  pressure  without  the  polishing  operation. 

Plate  finish  is  made  by  placing  the  paper  be  - 
tween  zinc  plates  and  subjecting  it  to  a heavy 
pressure.  This  does  not  give  as  fine  gloss  as  super- 
calendering,  but  makes  the  sheet  more  even  in 
thickness  and  well  adapted  for  fine  illustrations. 

Linen,  grain,  pebble,  and  “novelty”  finishes  are 
given  by  running  the  paper  between  rollers  or 
other  apparatus  which  have  their  surfaces  pre- 
pared to  impress  the  desired  pattern. 

CLASSES  OF  PRINTING  PAPER 

Papers  now  used  for  printing  are  divided  into 
four  general  classes,  viz. : writing  papers,  book 
papers,  cover  papers,  and  news.  These  are  again 
each  subdivided  into  a number  of  more  or  less 
specific  classes. 

Writing  papers  are  known  as  ledger,  bond, 
linen,  and  “fiat”  papers,  used  for  office  forms, 
stationery,  and  commercial  purposes.  The  qual- 
ity of  the  raw  material  ranges  from  new  linen 
rags  for  the  best  grades  down  to  wood  pulp  for 
the  cheaper  grades. 

Writing  papers  are  sized  with  a glutinous  prep- 
aration, made  of  animal  or  vegetable  fats,  to  give 
stiffness  to  the  paper  and  to  prevent  writing  ink 
from  spreading  on  it.  Size  may  be  mixed  in  the 
pulp  in  the  vat,  or  the  sheet  may  be  sized  by  pass- 
ing through  a bath  of  size,  when  it  is  said  to  be 


28 


MODERN  METHODS  OF  PRINTING 


tub-sized.  Highly  sized  paper  is  hard  and  does 
not  receive  the  impression  of  printing  ink  as 
readily  as  unsized  paper. 

Book  papers  embrace  a wide  range  in  quality, 
from  the  cheapest  wood  to  pure  linen  rag  stock. 
In  style  of  finish,  they  range  from  the  roughest 
antique  through  all  degrees  of  smoothness  to 
highly  polished  coated.  Sizing  is  used  in  some 
grades,  but  usually  it  is  unsized. 

In  book  papers  there  are  three  common  colors : 
natural,  white,  and  toned.  Natural  is  bleached 
pulp  without  adding  any  coloring  matter.  White 
is  made  by  adding  a small  quantity  of  bluing. 
Toned  color  (india  tint,  etc.)  is  produced  by  add- 
ing some  reddish  or  orange  coloring  matter. 

Cover  papers  are  made  of  rag  and  wood  pulps, 
usually  heavier  and  stronger  than  common  print- 
ing paper,  and  colored  in  endless  varieties,  for 
the  most  part  in  dark  colors,  and  finished  in  sur- 
faces from  the  highest  glaze  to  that  of  the  rough- 
est fabric.  For  convenience  in  handling,  as  well 
as  because  of  the  relatively  smaller  quantities 
used,  it  is  made  in  smaller  sheets  than  book  paper. 

RELATION  OF  PAPER  TO  PRINTING  METHOD 

The  adaptability  of  paper  to  any  special  printing 
method  depends  largely  upon  the  surface  and  to 
a lesser  degree  upon  the  character  of  the  paper 
stock.  A relief  printing  form  requires  relatively 
little  ink  and  little  pressure  in  order  to  leave  its 


MODERN  METHODS  OF  PRINTING 


29 


full  impress  upon  a smooth  paper.  As  the  paper 
becomes  rougher,  more  ink  is  needed  to  fill  up 
the  small  pores  of  the  surface  and  more  pressure 
to  force  the  ink  into  the  rough  surface.  On  a 
smooth  paper,  also,  the  relief  hair-line  leaves  the 
impress  of  its  face  only ; when  the  printing  form 
is  forced  into  a rough  surface  the  sides  of  the  lines 
show  more  or  less,  and  consequently  give  a thicker 
impression.  So  that  the  principle  holds,  in  relief 
printing,  that  the  finer  the  lines  the  smoother  the 
surface  must  be  to  print  clearly. 

Soft,  unsized  paper  takes  the  inked  impression 
with  relative  ease;  when  it  is  slightly  damp  it 
takes  impression  still  easier.  When  paper  is  well 
sized,  as  in  writing  paper,  the  increased  hardness 
makes  it  more  difficult  to  print;  it  then  needs 
stronger  impression  and  also  an  ink  with  in- 
creased adhesiveness  in  order  to  cling  to  the 
harder,  less  absorbent  surface. 

For  intaligo  printing  only  the  better  qualities 
of  paper  are  suited,  and  these  are  of  medium 
rough  finish.  Coated  or  enameled  papers  are  not 
at  all  suitable. 

For  lithographic  printing  the  paper  is  made 
smooth  (not  polished)  and  soft,  yet  strong  and 
with  a small  quantity  of  sizing.  For  lithographed 
labels  and  similar  work  the  paper  is  finished  on 
one  side  only. 

By  the  offset  printing  method  delicately  toned 
pictures  may  be  printed  on  rough  surfaces.  One 


30 


MODERN  METHODS  OF  PRINTING 


of  the  advantages  of  this  method  is  that  fine  pic- 
tures may  be  printed  on  a rough  surface  and  give 
all  the  softness  of  photographic  printing. 

The  condition  of  the  paper  at  the  time  of  print- 
ing is  always  a matter  for  consideration  in  care- 
ful presswork,  especially  in  the  case  of  work  done 
in  several  colors.  Paper  will  expand  in  moist  at- 
mosphere and  contract  when  exposed  to  dry  air. 
When  the  sheets  must  go  through  the  press  sev- 
eral times  and  the  atmosphere  of  the  workroom 
varies  from  dampness  to  dryness,  or  vice  versa, 
the  condition  of  the  paper  often  will  change 
enough  to  cause  many  difficulties. 

PRINTING  INK 

In  a general  way,  printing  ink  is  a combination 
of  boiled  oil  and  a black  or  colored  pigment.  It  is 
not  like  writing  ink,  but  is  more  like  paint,  with 
certain  qualities  which  are  necessary  for  its  par- 
ticular uses.  It  must  distribute  in  a thin  film  and 
it  must  work  clean,  with  a certain  tackiness  and 
without  spreading  away  from  the  parts  to  which 
it  is  applied  ; it  must  adhere  to  the  printing  sur- 
face readily,  and  yet  come  off  as  readily  and  ad- 
here to  the  paper;  it  must  not  dry  too  quickly 
while  being  used,  but  it  must  dry  reasonably 
hard  within  a short  time  after  being  applied  to 
the  printed  surface. 

The  best  inks  are  made  with  boiled  linseed 
oil ; others  have  linseed  and  rosin  oils  combined, 


MODERN  METHODS  OF  PRINTING 


31 


and  rosin  oil  only  is  used  for  the  cheaper  grades. 
Different  pigments  have  been  used  for  black 
ink  — black  minerals,  lampblack,  ivory  black  and 
carbon  black  — but  carbon  black  is  now  mostly 
used  because  of  its  density  and  covering  qualities. 
Sometimes  a touch  of  blue  pigment  is  added  to 
give  black  ink  a deeper  color. 

In  making  colored  inks,  the  pigments  are  ob- 
tained from  mineral  vegetable,  and  animal  sub- 
stances, each  of  these  furnishing  certain  colors 
well  adapted  for  special  purposes.  Almost  all 
colors,  however,  can  now  be  made  artificially 
from  coal-tar  dyes,  and  these  are  used  to  a great 
extent  in  the  ordinary  grades  of  printing. 


Composition  and  presswork  by  pupils  in  the  School  of  Printing, 
North  End  Union,  Boston,  1913. 


